1. Field of the Invention
The present invention relates to a tape drive controlling device suitable for use in a magnetic-tape transporting system of, for example, a video tape recorder (hereinafter referred to as a "VTR").
2. Description of the Related Art
A magnetic recording and reproducing apparatus using a magnetic tape (hereinafter referred to as a "tape") which is one kind of electronic apparatus provided with such a controlling device, particularly a video tape recorder for business use which is called a "VTR", has conventionally been provided with a shuttle function, i.e., the function of feeding the tape at a high speed while reproducing recorded images one after another for the purposes of cueing or the like during editing.
A typical arrangement of the shuttle function is such that when the travel speed of the tape is to be changed, an operator turns a jog dial to change the travel speed of the tape step by step. In this arrangement and in general, in a low-speed range, the tape is fed by the rotation of a capstan with a pinch roller pressed in contact with the capstan, while, in a high-speed range, the tape is fed by reels with the pinch roller away from the capstan.
However, since the conventional example is arranged in the above-described manner, a number of problems arise. For example, when tape feed is to be switched from capstan feed to reel feed or vice versa in a high-speed travel mode, the operation of bringing the pinch roller into or out of contact with the capstan is needed. This operation hinders smooth change of tape travel speeds, and a considerably long time is taken until a desired speed is reached. Particularly during a transition from the reel feed to the capstan feed, the tape is nipped between the pinch roller and the capstan with the result that the tape feed must be temporarily stopped. This leads to the problem that an image reproducing operation is temporarily stopped.
Another problem may occur during the reversal of a tape travel. This problem will be described below with reference to FIG. 1.
In FIG. 1, a drum provided with a recording and reproducing head is denoted by reference numeral 1, a supply reel by reference numeral 2, a take-up reel by reference numeral 3, a magnetic tape by reference numeral 4, tension detectors for detecting the tension of the tape 4 by reference numerals 5 and 6, and a speed detector for detecting the travel speed of the tape 4 by reference numeral 18.
The magnetic tape 4 is fed from the supply reel 2 to the take-up reel 3 during fast forward feed. A supply-reel motor 17 and a take-up-reel motor 14 directly drive the supply reel 2 and the take-up reel 3, respectively.
The tensions of the tape 4 on a supply side and a take-up side are respectively detected by the tension detectors 5 and 6 and supplied to terminals a and b of the selecting switch 7. The selecting switch 7 is interlocked with selecting switches 10 and 11, and when the tape 4 is to be made to travel in the forward direction (when the tape 4 is to be fed from the supply reel 2 and wound around the take-up reel 3), the signal at the terminal a is selected, while when the tape 4 is to be made to travel in the opposite direction, i.e., in the rearward direction, the signal at the terminal b is selected.
The output from the selecting switch 7 is compared with a tension reference value 9 in a subtracter 8, and an error with the tension reference value 9 is supplied to the terminal b of the selecting switch 10 and to the terminal a of the selecting switch 11.
When the tape 4 is to be made to travel in the forward direction, the selecting switch 7 selects and outputs the signal at the terminal a, and the tension error signal from the subtracter 8 is inputted to a loop filter 15. When the tape 4 is to be made to travel in the rearward direction, the selecting switch 7 selects and outputs the signal at the terminal b, and this signal is inputted to a loop filter 12. Each of the loop filters 12 and 15 performs phase compensation and gain compensation to stabilize an associated servo loop. The outputs from the loop filters 12 and 15 are inputted to reel motor drivers 13 and 16, respectively, and the reel motors 14 and 17 are driven by the associated reel motor drivers 13 and 16.
The output from the speed detector 18 is compared with a speed reference value 20 in a subtracter 19, and the obtained speed error is supplied to the terminal a of the selecting switch 10 and to the terminal b of the selecting switch 11.
In the above-described arrangement, the supply reel 2 is controlled so that the tape tension on the supply side reaches the reference tension value, while the take-up reel 3 is controlled so that the tape 4 is made to travel at a reference speed. Accordingly, it is possible to feed the tape 4 at a desired speed by changing the speed reference value.
However, the above-described conventional example has a number of problems. For example, when the direction of tape feed is changed, a tension control loop and a speed control loop are switched between the supply side and the take-up side with the result that an abnormally high or low tension which may damage the tape is instantaneously applied to it. It has, therefore, been difficult to stabilize the tape tension and smoothly change the direction of tape feed.